The present invention relates to a silver halide emulsion and, more particularly, to a tabular silver halide emulsion which contains iodide ions at a high concentration in an outer peripheral portion of a grain and has an average projected area diameter of 0.08 .mu.m to 0.5 .mu.m and an aspect ratio of 2 to 30.
The roughness (graininess) of images of color photographic light-sensitive materials, particularly, color reversal photographic light-sensitive materials often used by professional photographers is especially conspicuous in a bright portion (highlight portion) of an image. This portion is formed by relatively small silver halide emulsion grains contained in the lowest-speed one of sensitive layers of each color. To improve the graininess brought about by a silver halide emulsion containing grains in a small-size region, it is necessary to minimize the silver halide grain size required to obtain the same sensitivity. That is, a sensitivity increasing technique which compensates for a decrease in the sensitivity caused by a decrease in the grain size is necessary. U.S. Pat. Nos. (to be also referred to as US hereinafter) 4,434,226, 4,439,520, 4,414,310, 4,433,048, 4,414,306, and 4,459,353 have disclosed a sensitivity increasing technique which improves the color sensitization ratio by spectral sensitizing dyes by increasing the surface of a grain for receiving light by using a tabular silver halide grain. U.S. Pat. Nos. 4,672,027 and 4,693,964 have disclosed tabular grains having an aspect ratio of 8 or more and an average diameter of 0.2 to 0.55 .mu.m. Jpn. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-)62-18555 has disclosed that a photographic light-sensitive material that is excellent in sharpness can be obtained by an emulsion containing silver halide grains having a thickness of less than 0.12 .mu.m, an average diameter of less than 0.6 .mu.m, and an aspect ratio of 5 or more. The present inventors have studied grains having an average projected area diameter in the range of 0.5 .mu.m or less and an aspect ratio of 2 or more and confirmed that as the aspect ratio is increased, it is possible to use a larger amount of sensitizing dyes and raise the spectral sensitivity. On the other hand, it is found that the graininess deteriorates as the aspect ratio is increased, and as a consequence the total performance (sensitivity/graininess ratio) cannot be improved. Accordingly, a technique which improves the sensitivity/graininess ratio of tabular silver halide grains in a small-size region has been desired.